Studies on modifications on the internal cranial morphology in the evolution of anthropoid orbits

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Variations in the paranasal sinus anatomy of extant and fossil anthropoid primates have been extensively examined using computed tomography (CT), and have potential utility for phylogenetic analyses. We used this approach to evaluate the anatomy in 18 genera of extant strepsirrhines housed in the Primate Research Institute, Kyoto University and the University of Zurich, Switzerland. The maxillary sinus is formed in all the genera. The lorisiforms have an additional pseudo-ostium opening to the nasal cavity. In Propithecus, the inferior meatus expands laterally in the region anterior to this sinus, as seen in Gorilla and Pithecia, and the maxillary sinus is segmented into three distinct chambers which have openings to the middle meatus, respectively. In Eulemur, an additional sinus-like cavity is formed in the region posterior to this sinus. Sphenoidal pneumatization with an opening to the ethmoidal region is found in all the genera, despite of differences in volume. Distinct patterns o … More f pneumatization of the frontal region are found in Eulemur, Daubentonia, Indri, Propithecus, and Avahi. The frontal sinus in Avahi communicates with the maxillary sinus. In many of the other genera, a small cavity expanding from the ethmoidal region is formed in the circumfrontal-ethmoidal region, and this feature is probably homologous to the frontal sinus. The paranasal sinuses are more variable in form in the Indridae than in the other families. The present study confirms the view that the lack of paranasal sinuses in the Old World monkeys is quite unique among the order Primates. The maxillary sinus expanding laterally into the space between the orbital floor and molar alveolar is structurally accompanied with the inferior rotation of the lower facial part against the orbital-cranial region. Such a modification contributes to the frontation of the orbits. Thus, the degree in lateral expansion of the maxillary sinus could be available for examining the orbital anthropoidization in fossil specimens. Less